1. Field of the Invention
The present invention relates to systems for feeding and transporting documents and to a method and system for document overlap/gap error detection and correction.
2. Background Art
A typical system for feeding and transporting documents includes a feeder and a separator in the document feeding portion of the system, and a series of roller pairs or belts in the document transporting portion of the system. In the feeding portion of the system, the feeder acts with the separator to feed documents singly, in order, from a stack. In the transporting portion of the system, the roller pairs and/or belts convey the documents, one at a time, past other processing devices such as readers, printers, and sorters that perform operations on the documents. The feeder is typically a feed wheel, but may take other forms. The separator may be a wheel, but also may take other forms such as a belt. Further, the components in the transporting portion of the system may take a variety of forms. Systems also include a component in the document feeding portion of the system that nudges documents into the nip between the feeder and the separator. A suitable nudger may be a nudger wheel, but may take other forms. An existing document feeder is shown in U.S. Pat. No. 6,199,854. That patent describes a document feeder with a variable speed separator.
In systems for feeding and transporting documents, it is critical that there is sufficient space between documents so that each document can be detected individually and processed by processing devices downstream of the initial roller pairs and/or belts of the transporting portion of the system. For example, sufficient space between documents would be required so that each document can be detected individually and processed by a check sorter, imager, or printer. Some existing systems rely solely on the speed difference between the first document driver beyond the feeder, known as the document accelerator, and the feeder. That is, the accelerator runs at a higher peripheral speed than the feeder such that the documents become separated as the documents pass through the accelerator. This separation technique is completely mechanical, and although used in some applications that have been successful, does not account for the fact that documents are occasionally fed overlapped from the feeder.
Previous overlap correctors wait until the trailing edge of the first, leading, document reached a downstream sensor before attempting to correct the document spacing. U.S. Pat. No. 5,848,784 describes a document separation apparatus. That patent describes the downstream accelerator/deceleration of documents with pinch rollers to adjust document spacing. Although the downstream acceleration/deceleration of documents with pinch rollers to adjust document spacing is sufficient for many applications, in certain situations it would be desirable to measure an overlap sooner, that is, before the trailing edge of the first, leading, document reaches the downstream sensor, so that there is greater distance of the second, following, document remaining to perform the correction.
For the foregoing reasons, there is a need for an improved method and system for document overlap/gap error detection and correction.
It is, therefore, an object of the present invention to provide a method and system for document overlap/gap error detection and correction that may measure an overlap before the first document trailing edge arrives at the downstream edge detector.
In carrying out the above object, a method of document overlap/gap error detection and correction in a system for feeding and transporting documents is provided. Each document has a leading edge and a trailing edge. The system includes a feeder stage and a transport stage downstream of the feeder stage for receiving a document from the feeder stage. The feeder stage includes a controllable feeder and a separator for receiving the document therebetween. The system includes at least one edge detector between the feeder stage and the transport stage for detecting passing document edges during operation of the system. The method comprises detecting a trailing edge of a first document at the feeder, and detecting a leading edge of a second document at the at least one edge detector. The second document follows the first document and the second document is still received between the feeder and the separator when the second document leading edge is detected at the at least one edge detector. The method further comprises determining an overlap/gap error, if any, between the first document and the second document based on the first document trailing edge detection and the second document leading edge detection. The feeder is controlled to correct the overlap/gap error, when the error is present.
Embodiments of the present invention may determine the overlap/gap error in a variety ways. In one embodiment, determining the overlap/gap error further comprises, after detecting the first document trailing edge, operating the feeder at a constant velocity until detecting the second document leading edge. The overlap/gap error, if any, between the first document and the second document is determined based on an elapsed time between the first document trailing edge detection and the second document leading edge detection.
In another embodiment, determining the overlap/gap error further comprises providing a tachometer at the feeder, with the tachometer generating an output. The overlap/gap error, if any, between the first document and the second document is determined based on the tachometer output between the first document trailing edge detection and the second document leading edge detection. The tachometer may be implemented in any suitable way. For example, the tachometer may include an encoder and generate a pulse sequence as the tachometer output. For example, the tachometer may generate an analog velocity output as the tachometer output.
Further, in some embodiments of the present invention, the at least one edge detector is a single edge detector. In preferred embodiments, the at least one edge detector is a sequence of edge detectors. In a preferred embodiment that utilizes the sequence of edge detectors, the leading edge of the second document may be detected at an edge detector in the sequence at the same time as detecting the trailing edge of the first document at the feeder. That is, in single edge detector embodiments, moving the single edge detector closer to the feeder provides earlier detection. Moving the single edge detector closer to the transport stage, although providing slightly later detection, allows for detection of greater overlaps. The single sensor embodiments may be suitable for many applications depending on the range of expected overlaps and gaps and the extent that detection must occur early. Preferred embodiments that utilize a sequence of edge detectors to provide the advantages of being able to detect large overlaps and also provide early detection.
Further, in carrying out the present invention, a system for feeding and transporting documents is provided. Each document has a leading edge and a trailing edge. The system comprises a feeder stage, a transport stage, at least one edge detector, and control logic. The feeder stage includes a controllable feeder and a separator for receiving documents therebetween. The feeder stage is configured to detect a trailing edge of a first document at the feeder. The transport stage is downstream of the feeder stage for receiving documents from the feeder stage. The at least one edge detector is between the feeder stage and the transport stage for detecting passing document edges during operation of the system. Control logic is configured to determine an overlap/gap error, if any, between the first document and a second document following the first document based on the first document trailing edge detection and a second document leading edge detection at the at least one edge detector. The control logic is further configured to control the feeder to correct the overlap/gap error, when the error is present.
Embodiments of the present invention may determine the overlap/gap error in a variety of ways. For example, after the first document trailing edge is detected, the feeder may be operated at a constant velocity until the second document leading edge is detected. The overlap/gap error, if any, between the first document and the second document is determined based on an elapsed time between the first document trailing edge detection and the second document leading edge detection. Further, for example, the system may include a tachometer at the feeder with the tachometer generating an output. The control logic would then be further programmed to determine the overlap/gap error based on the tachometer output between the first document trailing edge detection and the second document leading edge detection. The tachometer may include an encoder and generate a pulse sequence as a tachometer output. Or, the tachometer may generate an analog velocity output as the tachometer output. In addition, systems for feeding and transporting documents in accordance with the present invention may utilize a single edge detector or a sequence of edge detectors, and in the preferred embodiment, a sequence of edge detectors is used.
The advantages associated with embodiments of the present invention are numerous. For example, embodiments of the present invention provide methods and systems for document overlap/gap error detection and correction that measure overlap before the trailing edge of the first document reaches the edge detector downstream of the feeder. The earlier calculation of overlap/gap error leaves a greater distance of the second document with which to perform any correction. Correction is performed by controlling the feeder. Earlier determination of the overlap/gap error may allow for reduced motor requirements for the feeder because earlier detection increases the amount of distance remaining of the second document that is still in the feeder with which to perform correction.